Crystal material, scintillator, and radiation detector

Abstract

This crystal material is an oxide single crystal that is represented by chemical formula (1): M3(Ta1−xNbx)O5, and that has a cubic crystal structure and has a density of 8.0 g / cm3 or greater. In the chemical formula, M is at least one element selected from rare earth elements, and 0≤x≤1. The crystal material is a high-melting-point material having a melting point of 2000°C or higher. A radiation detector (100) can be configured from a scintillator (101) that is configured from the crystal material, and a photodetector (102) that receives scintillation light from the scintillator (101).

Description

Crystalline materials, scintillators, and radiation detectors

[0001] The present invention relates to a crystalline material, a scintillator, and a radiation detector.

[0002] Measurement of gamma rays, X-rays, alpha rays, beta rays, neutron rays, etc. is an important technology. Scintillators are used for this type of measurement. In particular, high-density scintillator crystals have the following properties when irradiated with radiation, typically gamma rays: a) high radiation stopping power, b) large effective atomic number, and c) high density. High-density scintillator materials are expected to be used as scintillator materials in Cherenkov detectors and cosmic ray radiation detectors.

[0003] Furthermore, in radiation detectors used in medical equipment, scintillator materials having the above-mentioned properties can achieve high detection performance due to their high radiation stopping power, and are expected to have effects such as shortening measurement time and radiation exposure time. Here, when used as a scintillator material, it is preferable that the scintillator material has a higher luminescence output and high energy resolution, and for this reason, it is suitable that the scintillator material be used as a transparent single crystal without impurities.

[0004] Scintillator materials with particularly high densities and effective atomic numbers are used to detect high-energy radiation, and are installed in detectors for cosmic ray measurements and high-energy experiments using accelerators, etc. Currently, PbWO4 single crystal (density: 8.28 g / cm3), which has the highest density of any existing scintillator material, is 3 ) is widely used (Non-Patent Documents 1 and 2).

[0005] Michiko Morooka et al., "Characteristics of Radiation Damage in Lead Tungstate (PbWO4) Heavy Crystal Scintillator," Bulletin of the Faculty of Engineering, University of Miyazaki, edited by the Faculty of Engineering, University of Miyazaki, No. 28, pp. 297-301, 1999. Masaaki Kobayashi, "Recent Developments in Inorganic Crystal Scintillators," High Energy Physics Researchers Conference, High Energy News Research Introduction, Vol. 21, No. 2, pp. 41-50, 2002, [Retrieved April 20, 2022] (http: / / www.jahep.org / hepnews / 2002 / Vol21No2-2002.6.7kobayashi.pdf).

[0006] However, as accelerator energy and beam intensity increase, there is a demand for even higher density scintillator materials. In addition, because PbWO4 contains a high concentration of Pb, which is an environmentally hazardous substance, there is a demand for new lead-free, high-density scintillators.

[0007] The present invention has been made to solve the above problems, and has as its object to provide a lead-free, higher density crystalline material that can be used as a scintillator material.

[0008] The crystalline material according to the present invention has the chemical formula M3 (Ta 1-x Nb x ) O5, has a cubic crystal structure and a density of 8.0 g / cm 3 In the above-described oxide single crystal, M in the chemical formula is at least one element selected from rare earth elements, and 0≦x≦1.

[0009] In one example of the above-mentioned crystal material, a rare earth element that serves as a luminescence center is further added.

[0010] The scintillator according to the present invention is made of the above-mentioned crystalline material.

[0011] A radiation detector according to the present invention includes a scintillator made of the above-described crystalline material, and a photodetector that receives scintillation light from the scintillator.

[0012] As described above, according to the present invention, M (Ta) is at least one element selected from rare earth elements. 1-x Nbx ) The density of O5 is 8.0 g / cm 3 By using the above-described single crystal, a lead-free, higher density crystal material that can be used as a scintillator material can be provided.

[0013] FIG. 1 is a diagram showing the configuration of a radiation detector 100 according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of a micro-pulling down furnace. FIG. 3 is a photograph of Sample 1 of Example 1. FIG. 4 is a photograph showing the structure of Sample 1 of Example 1 observed using a scanning electron microscope. FIG. 5A is a characteristic diagram showing the results of phase identification by X-ray diffraction (XRD) measurement of Sample 1 of Example 1. FIG. 5B is a photograph showing the results of Laue image measurement performed using a back-reflection Laue camera on cut and polished Sample 1 of Example 1. FIG. 6 is a characteristic diagram showing the results of emission spectrum measurement of each sample prepared in the examples. FIG. 7 is a photograph of Sample 2 of Example 2. FIG. 8 is a photograph of Sample 3 of Example 3. FIG. 9 is a characteristic diagram showing the results of transmission spectrum measurement of Sample 1. FIG. 10 is a characteristic diagram showing the results of X-ray radioluminescence measurement of Sample 2. FIG. 11A is a photograph of a sample in which 1 mol % Tb is added to the Lu site of a Lu3TaO7 sample. Fig. 11B is a photograph of a sample in which 1 mol% Tm was added to the Lu site of a Lu3TaO7 sample. Fig. 12A is a characteristic diagram showing the results of XRD measurement of a sample in which 1 mol% Tb was added to the Lu site of a Lu3TaO7 sample. Fig. 12B is a characteristic diagram showing the results of XRD measurement of a sample in which 1 mol% Tm was added to the Lu site of a Lu3TaO7 sample. Fig. 13A is a characteristic diagram showing the results of X-ray radioluminescence measurement of a sample in which 1 mol% Tb was added to the Lu site of a Lu3TaO7 sample. Fig. 13B is a characteristic diagram showing the results of X-ray radioluminescence measurement of a sample in which 1 mol% Tb was added to the Lu site of a Lu3TaO7 sample.

[0014] The crystal material according to the embodiment of the present invention will be described below. This crystal material has the chemical formula M3 (Ta 1-x Nb x ) O5 ... (1), has a cubic crystal structure, and has a density of 8.0 g / cm 3The oxide single crystal is one of the above. Here, M in the chemical formula is at least one element selected from rare earth elements, and 0≦x≦1. This crystalline material is a high-melting point material with a melting point of 2000°C or higher. For example, M in the chemical formula can be at least one element selected from Lu, Gd, and La.

[0015] The crystalline material according to the above-described embodiment can be used as a scintillator material. A radiation detector 100 can be configured by a scintillator 101 made of the crystalline material according to the embodiment and a photodetector 102 that receives scintillation light from the scintillator 101 ( FIG. 1 ). The crystalline material according to the embodiment has high radiation blocking performance and a high refractive index. The crystalline material according to the embodiment can be formed to any thickness, depending on the crystal growth method.

[0016] For example, to obtain a single crystal of a crystalline material with the chemical formula LuTaO, LuO and TaO can be used as raw materials in a ratio of LuO:TaO = 75:25. The melting point of LuTaO is approximately 2400°C (Reference 1). To obtain a single crystal of a crystalline material with the chemical formula LuNbO, LuO and NbO can be used as raw materials in a ratio of LuO:NbO = 75:25. The melting point of LuNbO is approximately 2030°C (Reference 2).

[0017] To obtain a good single crystal, it is preferable to produce it with approximately the above composition. These compositions correspond to the congruent melting composition. However, it is not necessary to completely deviate from the above composition; a range of ±5 mol% from the congruent melting composition is acceptable. More preferably, a range of ±2 mol% is acceptable. The reason for limiting the ranges near these compositions is that, when each composition is near the congruent melting composition during single crystal growth, a single crystal with a solid solution region can be obtained. However, if the composition deviates from other composition ranges, i.e., by 5 mol% or more, one phase will crystallize first, disrupting the single crystal structure.

[0018] However, since there is a measurement error in the eutectic composition exemplified above, it is important that the composition is within ±2 mol% of the congruent melting composition, but it may deviate by about ±5 mol% if a substantially good structure is obtained. Similarly, the melting point mentioned above is also shown to be near the above temperature due to measurement error, and does not impose any limitations.

[0019] The crystalline material according to the embodiment emits light when excited by radiation. In particular, in order to increase the luminous efficiency, it is possible to add a component (rare earth element) that becomes the luminescence center to the base material constituting the crystalline body, and also to subject the base material to oxidation / reduction treatment.

[0020] A number of additive elements for controlling the light-emitting characteristics can be selected depending on the application, and a single element or multiple elements can be added. The additive elements can be selected from rare earth elements such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. When adding the above elements, they can be appropriately selected to meet requirements such as light emission intensity, emission wavelength, fluorescence lifetime, and energy resolution depending on the application. The amount of each additive element added can also be appropriately selected depending on the application.

[0021] Also, the chemical formula M3 (Ta 1-x Nb x The rare earth element M in O5 and the additive element for controlling the luminescence characteristics have different effects, so they can be selected independently according to requirements. By selecting the rare earth element M, the base material M3 (Ta 1-x Nb x ) The band structure of O5 can be controlled to realize efficient energy transfer from the host material to the additive element during radiation excitation. On the other hand, the additive element for controlling the luminescence characteristics can control the wavelength, fluorescence lifetime, and luminescence intensity of the luminescence generated by radiation excitation.

[0022] Nb can be added to the Ta site depending on the application, and the amount of Nb added can also be appropriately selected depending on the application. It is also possible to replace all Ta with Nb.

[0023] When using this type of crystalline material as a scintillator material, it is preferable that it has a higher light output and a higher energy resolution, and for this reason, it is preferable that the material be used as a transparent single crystal without impurities. The performance of a scintillator is greatly influenced by its radiation stopping power. The radiation stopping power is a value determined by the density and effective atomic number, and generally, the radiation stopping power improves by increasing the density and effective atomic number.

[0024] For example, rare earth tantalates, which have the chemical formula RE3TaO7 (RE is a rare earth element), are attracting attention as scintillators with high radiation stopping power because they are materials with high density and effective atomic number. Most scintillators must extract the light generated by radiation exposure to the outside, and in order to extract the light efficiently without attenuation, they are used as single crystals that are transparent at the emission wavelength of the light.

[0025] However, RE3TaO7 has a melting point exceeding 2200° C. Therefore, when a single crystal is grown by a conventional melt growth technique using a noble metal crucible, the crystal growth temperature exceeds the operating temperature of the platinum or iridium that constitutes the crucible, and therefore it has not been possible to grow (grow) a single crystal of RE3TaO7.

[0026] On the other hand, attempts have been made to grow single crystals of materials with melting points above 2200°C using melt growth methods using molybdenum crucibles, tungsten crucibles, and rhenium crucibles. However, because the crucible materials molybdenum, tungsten, and rhenium are more easily oxidized than platinum and iridium, the growth atmosphere must be reduced, and growth has been carried out in an argon atmosphere containing 2% or more hydrogen. However, crystal growth in a reducing atmosphere can cause damage to the crucible, and there is a risk that the melt of the material to be grown may react with the crucible during crystal growth, that the crucible material may become mixed into the crystal, or that the raw material may decompose in a reducing atmosphere. Therefore, this method has been limited to very limited systems, such as sesquioxide-based systems and sapphire single crystals.

[0027] Furthermore, due to the recent rise in the price of rhenium, the cost of rhenium crucibles has risen to several to several dozen times that of platinum or iridium crucibles, making them unsuitable as a method for producing commercial single crystals.

[0028] One technique to solve the above problems is to use a tungsten crucible with deoxidized zirconia heat insulating material in an inert atmosphere and grow a crystal by unidirectional solidification of the raw material melt contained in the tungsten crucible. This crystal growth method using a tungsten crucible with deoxidized zirconia heat insulating material in an inert atmosphere can grow a single crystal of RETaO with a high melting point.

[0029] This crystal growth method comprises the following steps: a first step of mixing materials for forming a single crystal having a high melting point, such as RE3TaO7; a second step of deoxidizing an insulating material in a high-temperature inert atmosphere in a carbon furnace; a third step of melting the material for forming a single crystal having a high melting point, which is filled in a tungsten crucible, using the deoxidized insulating material; and a fourth step of solidifying the molten material having a high melting point in one direction to produce a single crystal.

[0030] By growing the crystal in this manner, it is possible to produce a scintillator crystal having a high density and a high melting point of 2100° C. or higher. In this crystal growth method, the use of a deoxidized heat insulating material prevents deterioration of the tungsten crucible and enables crystal growth while suppressing reaction between the molten raw material and the crucible, making it possible to grow crystals at temperatures exceeding 2100° C., which was not possible with conventional crystal growth using platinum or iridium crucibles.

[0031] Next, a method for producing a crystal material (crystal growth method) according to the above-described embodiment will be described.

[0032] First, in the first step, materials constituting the crystalline phase are mixed to form a raw material. Next, in the second step, the prepared raw material is melted. The raw material can be melted, for example, using a predetermined crucible. Next, in the third step, the melted raw material is solidified along one direction to generate a crystalline body (crystalline material).

[0033] The method for producing crystalline materials can be any method (crystal growth method) that melts and solidifies the desired material system with an optimal composition and unidirectional orientation. In particular, it is required to control the temperature gradient to achieve stable crystal growth, and it is preferable to perform the process under conditions where the temperature gradient at the solid-liquid interface of the mixture is 10°C / mm or more. However, to eliminate cracks due to thermal stress on the crystal, the temperature gradient can be reduced within a reasonable range. Furthermore, cracks can be suppressed by reheating the already crystalline portion to a degree that does not melt it.

[0034] Next, an apparatus (micro-pulling furnace) for carrying out the production (crystal growth) of a crystalline material according to an embodiment will be described with reference to Fig. 1. In the micro-pulling method, a raw material 203 is placed in a crucible 201 with a hole in the bottom, and the crucible 201 is heated by high-frequency induction heating using a high-frequency induction coil 202. The molten raw material 203 is then pulled down from the bottom of the crucible 201 using a seed crystal or the like, thereby forming a solid-liquid interface directly below the bottom of the crucible 201. This method is suitable for growing crystals of crystalline materials with high melting points. The crucible 201 can be made of tungsten.

[0035] This apparatus includes a high-frequency induction coil 202 whose length is comparable to that of the crucible 201, and a heat insulator 204 for realizing a temperature gradient of 10°C / mm or more at the solid-liquid interface of the raw material 203, which is a mixture. The molten liquid at the bottom of the crucible 201 is pulled downward by a tungsten seed rod 205 installed below the crucible 201, thereby solidifying in one direction. Note that a seed crystal can be used instead of the seed rod 205. The seed rod 205 is fixed to the upper end of a rod 207, and the seed rod 205 can be pulled down by pulling down the rod 207 with a pulling-down mechanism (not shown).

[0036] Furthermore, the temperature gradient at the solid-liquid interface can be controlled to an optimum value for crystal production by using an afterheater 206 installed below the crucible 201. Furthermore, a manufacturing method employing an equivalent mechanism is also possible. However, if the solid-liquid interface can be made smooth, the temperature gradient can be made less than 10°C / mm. The crucible 201, high-frequency induction coil 202, heat insulator 204, seed rod 205, and afterheater 206 are placed in a chamber 208.

[0037] Crystals can also be produced by crystal pulling, as in the Czochralski method. This method is preferable because it allows for the production of large crystals, as opposed to the micro-pulling-down method, which involves pulling the crystal downward. Crystals can also be produced in a crucible, as in the Bridgman method. This method is preferable because large crystals can be produced with a high yield by optimizing the production conditions. Crystals can also be produced by the floating zone method. This method is preferable because it does not require the use of a crucible, there is no contamination of impurities from the crucible, and the cost of the crucible is eliminated. Crystals can also be produced by crystal pulling using a die, as in the edge-defined film-fed growth (EFG) method. This method is preferable because it allows for the shape of the sample to be produced to be controlled.

[0038] Next, we will discuss the composition of the raw materials used to prepare the crystal. The composition of the raw material used to prepare the crystal according to the above-described embodiment can deviate by more than ±5 mol%. In other words, in the case of the micro-pulling-down method, if the entire raw material is melted and then unidirectionally solidified downward in the crucible, the material with the target composition will crystallize first from the beginning of solidification, and the composition of the remaining melt will gradually change. As a result, the composition of the raw material melt reaches the eutectic point in the latter half or final stage of solidification, and a phase with a composition different from the target composition will phase separate and precipitate together with the target composition. The precipitated unnecessary portion can be simply cut off after the crystal is prepared.

[0039] The crystalline material according to the embodiment can be used in combination with an electron multiplier tube or an MPPC (Multi-Pixel Photon Counter), which are elements that perform photoelectric conversion, as a radiation detector used in environmental measurement, medical equipment, etc. In particular, the scintillator made of the crystalline material according to the embodiment has high density, and therefore can be applied to situations that require the detection of higher energy radiation, measurement in a short time, and the use of Cherenkov light due to a high refractive index.

[0040] Furthermore, since there is no need to make the raw materials nanoscale or to make the particle size uniform when producing the crystalline material, it can be produced at a lower cost than conventional transparent ceramic materials, and since it does not suffer from the problem of the decrease in transmittance that occurs with larger sizes, which is a problem with transparent ceramics, it is also suitable for use in situations where lower costs and larger sizes are required.In the above applications, it is also possible to adjust the properties to suit the required characteristics by adding other materials and controlling the amount of addition.

[0041] The following will explain in more detail using examples.

[0042] Example 1 First, Example 1 will be described. First, raw material powders of Lu2O3 and Ta2O5 were weighed out in a molar ratio of Lu2O3:Ta2O5 = 3:1 and mixed in an agate mortar to prepare a powder. The prepared mixed powder was sintered multiple times in an electric furnace using an alumina crucible at a temperature of 1200°C to obtain a sintered body (raw material) of Lu3TaO7. The obtained raw material was placed in a tungsten crucible 201 used for crystal growth. The crucible 201 used had a φ3 mm die on the bottom surface and a 0.5 mm capillary in the center of the die.

[0043] Next, the crucible 201 containing the raw material was placed above the afterheater 206, and the high-frequency induction coil 202 was operated to heat the raw material contained in the crucible 201 to a temperature of 2400°C or higher. This completely melted the raw material contained in the crucible 201. After this, the melt of the raw material contained in the crucible 201 (raw material melt) passed through the capillary at the bottom and appeared on the die bottom surface of the crucible 201, wetting and spreading. The wetted and spread raw material melt was brought into contact with the seed rod 205, and the raw material melt was pulled downward together with the seed rod 205, forming a solid-liquid interface directly below the bottom surface of the crucible 201, and the raw material melt was unidirectionally solidified. The raw material melt was pulled down at a rate of approximately 0.1 to 5 mm / min.

[0044] In this way, the raw material melt was solidified in one direction directly below the crucible 201 to produce a rod-shaped crystal (crystalline material). The obtained crystal, which is Sample 1 of Example 1, is shown in Fig. 3(a). Sample 1 was cut perpendicular to the growth direction and the cut surface was optically polished to produce Sample 1 for evaluating physical properties, which is shown in Fig. 3(b).

[0045] The polished surface of Sample 1 thus prepared was subjected to a scanning electron microscope (SEM) and an energy dispersive X-ray spectroscopy (EDX) method to observe the structure and analyze the composition of a local region. As a result, Sample 1, a crystalline body obtained, was found to be composed of a single phase containing only La, Ta, and O, and the presence of other phases was not confirmed. Furthermore, as shown in Figure 4, the presence of grain boundaries was not confirmed in the structural observation using the scanning electron microscope.

[0046] Furthermore, the phase of Sample 1 prepared in Example 1 was identified by X-ray diffraction (XRD) measurement, and as a result, all diffraction peaks were identified as cubic systems of the space group of LuTaO, and no impurity phases were confirmed, as shown in Figure 5A. These results indicated that the crystalline body prepared in Example 1 was a single phase of LuTaO.

[0047] Furthermore, a Laue image of the cut and polished sample 1 was measured using a back-reflection Laue camera, and clear Laue spots were confirmed, as shown in Fig. 5B. Furthermore, this measurement allowed the confirmed Laue spot pattern to be identified as a cubic space group system, indicating that the prepared LuTaO crystal was a single crystal.

[0048] Example 2 Next, Example 2 will be described. Example 2 shows the effect of controlling the luminescence characteristics by Nb substitution at the Ta site in LuTaO prepared in Example 1. First, in Sample 1 prepared in Example 1, which did not contain any additive elements, the emission spectrum measurement showed strong, sharp emission near 290 nm and weak, broad emission near 360 nm, as shown by the white circle (no additive) in Figure 6.

[0049] Next, by the same manufacturing method as in Example 1, Lu3TaO7 was fabricated by substituting 10 mol % Nb for the Ta site. 0.9 Nb 0.1 A crystal of La, Ta, Nb, and O was prepared as Sample 2 (FIG. 7). When Sample 2 of Example 2 was subjected to phase analysis by XRD measurement in the same manner as described above, it was found to have a single phase similar to Sample 1 containing no added elements, and composition analysis using EDX revealed that it was composed of a single phase containing only La, Ta, Nb, and O.

[0050] Furthermore, as a result of measuring the Laue image of Sample 2 using a back-reflection Laue camera, clear Laue spots were confirmed, and the pattern was identified as a cubic crystal orientation, demonstrating that Sample 2, a Nb-substituted LuTaO crystal, was a single crystal. Here, the substitution amount of the added element is not limited to 10 mol %.

[0051] Lu3(Ta) with 10 mol% Nb added (substituted) to the Ta site 0.9 Nb 0.1 When photoluminescence measurement was performed on Sample 2 of )O, it showed a clear emission peak near 290 nm (open triangle in Figure 6), similar to Sample 1 without any added element. This indicates that emission at 290 nm is maintained even when Nb is actually substituted.

[0052] Example 3 Next, Example 3 will be described. In Example 3, Sample 3 was prepared by the same preparation method as described above, in which 0.5 mol % of Ce was further added to the Lu site of LuTaO. As a result, the crystal shown in FIG. 8 was obtained, and XRD measurement, EDX composition analysis, and Laue image measurement revealed that it was a single crystal having the same crystal structure as undoped LuTaO (Sample 1).

[0053] Photoluminescence measurement of the Ce-doped LuTaO sample 3 showed a clear emission peak near 290 nm (white square in Figure 6), similar to the sample 1 without any added element. This indicates that the emission at 290 nm is maintained even when Ce is actually added.

[0054] Measurement of the transmission spectrum of the obtained LuTaO single crystal, Sample 1, showed a transmittance of 70% or more in the wavelength region of 450 nm or more, as shown in Figure 9, which is a high transmittance equivalent to that of other optical crystals. This high transmittance was also observed in crystals that were Nb-substituted or Ce-doped (Sample 2, Sample 3).

[0055] When the Nb-substituted Lu3TaO7 single crystal (sample 2) was subjected to X-ray radioluminescence measurement, light emission was confirmed in the vicinity of 350 nm as shown in Figure 10, indicating that light was emitted by irradiation with radiation.

[0056] Example 4 Next, Example 4 will be described. In Example 4, samples were prepared by the same preparation method as described above, in which 1 mol% of Tb or Tm was added to the Lu site of a LuTaO sample. As a result, the crystals shown in FIGS. 11A and 11B were obtained. FIG. 11A shows a sample in which 1 mol% of Tb was added to the Lu site of a LuTaO sample, and FIG. 11B shows a sample in which 1 mol% of Tm was added to the Lu site of a LuTaO sample.

[0057] XRD measurements, EDX composition analysis, and Laue image measurements of these samples revealed that they were single crystals with the same crystal structure as undoped Lu3TaO7. The results of XRD measurements of a sample with 1 mol% Tb added to the Lu site of the Lu3TaO7 sample are shown in Figure 12A. The results of XRD measurements of a sample with 1 mol% Tm added to the Lu site of the Lu3TaO7 sample are shown in Figure 12B.

[0058] Next, the results of X-ray radioluminescence measurements of each of the above samples are shown in Figures 13A and 13B. As shown in Figure 13A, in the Tb-doped Lu3TaO7 sample, an emission peak was clearly observed in the 500-600 nm range, which was not observed in the sample containing no added element. This result shows that by changing the added element, emission originating from each added element is observed.

[0059] As described above, according to the present invention, M (Ta) is at least one element selected from rare earth elements. 1-x Nb x ) The density of O5 is 8.0 g / cm 3 By using the above-described single crystal, it becomes possible to provide a lead-free, higher density crystal material that can be used as a scintillator material.

[0060] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0061] [Reference 1] X. Xing et al., "High-Temperature Phase Relations in the Lu2O3-Ta2O5 System", Journal of the American Ceramic Society, vol. 99, no. 3, pp. 1042-1046, 2016. [Reference 2] L. An et al., "Transparent Lu3NbO7 bodies prepared by reactive spark plasma sintering and their optical and mechanical properties", Ceramics International, vol. 39, pp. 383-387, 2013.

[0062] 100...radiation detector, 101...scintillator, 102...photodetector.

Claims

1. Chemical formula M 3 (Ta 1-x Nb x ) O 7 and has a density of 8.0 g / cm3 3 The oxide single crystal is as described above. In the above chemical formula, M is at least one element selected from rare earth elements, and 0≦x≦1.

2. The crystalline material of claim 1, Furthermore, the crystal material is doped with rare earth elements that act as luminescence centers.

3. A scintillator made of the crystal material according to claim 1 or 2.

4. A scintillator made of the crystal material according to claim 1 or 2; a photodetector that receives scintillation light from the scintillator; A radiation detector comprising:

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